This patch adds some infastructure for IndexedDB callbacks in V8.
It also adds a stub of IDBDatabaseRequest. In the near future,
I'll gut the event based implementation code, flesh out IDBReqest
further, and start plumbing IndexedDatabaseRequest.
Code is not testible because it doesn't work (yet).

Attachment 50294[details] did not pass style-queue:
Failed to run "WebKitTools/Scripts/check-webkit-style" exit_code: 1
WebCore/bindings/v8/custom/V8CustomIDBCallback.h:92: One space before end of line comments [whitespace/comments] [5]
Total errors found: 1 in 10 files
If any of these errors are false positives, please file a bug against check-webkit-style.